This invention relates to cinematographic systems and more particularly, it concerns a circuit for controlling the speed of a motor which advances a photographic film strip in an automatic film processing system.
U.S. Pat. No. 3,830,564 issued Aug. 20, 1974 to John F. Batter, Jr., No. 3,909,120 issued Sept. 30, 1975 to Joseph A. Stella and No. 3,941,465 issued Mar. 2, 1976 to Irwin E. Figge, et al are representative of a larger number of prior art disclosures directed to a motion picture system in which a cassette contained film strip may be exposed, processed and viewed by projection of successive image frames formed on the film strip without removal from the cassette, principally as a result of a one use processing facility provided in the cassette. The system represented by this prior art has evolved to a point where one desiring to take and view motion pictures need merely place the cassette in an appropriately designed motion picture camera, expose the film strip in traditional fashion, remove the cassette from the camera and place it in a viewer apparatus, operable upon rewinding the film strip to apply cassette contained processing fluid to the strip, and within minutes of time, view the motion pictures he has taken by projection of light through the processed film strip.
Because the exterior appearance of the cassette remains unchanged whether processed or unprocessed and also because the same cassette will be re-used to view the processed film strip after it has once been processed, the viewing apparatus is appropriately automated to discern the condition of the film strip in the cassette and to program respective process, project or rewind operational modes in accordance with the information provided by the condition of the film strip in the cassette. Also because the viewer represents a basic piece of equipment constituting a major portion of the system from a cost standpoint, it must be capable of operation as effective for repeated viewing of the film as it is for processing the film strip in the first instance. Furthermore, to be competitive with more traditional motion picture "projectors," the viewer as well as the cassette must be capable of accomodating such features as a motion picture "sound" capability.
Although the present state of the art relating to viewer/processors for such cinematographic systems has demonstrated functional viability, there is need for improvement particularly in the electro/mechanical organization of such equipment by which functional reliability of existing systems may be retained or improved but with lower manufacturing costs from the standpoint of both individual component manufacture and component assembly. Also such systems in general have developped to a point where the cassette contained film strip may be provided with a sound recording medium capable of use with a sound system in the viewer/processor. Problems have arisen, however, in reducing the manufacturing costs associated with providing a sound capability as an option to an existing "silent" viewer/processor design.
The present invention is incorporated in a viewing apparatus for multi-purpose photographic film cassettes of the type mentioned. Automated programming of diverse operating modes is effected by a programming cam disc in combination with an electronic logic system enabling the use of a single drive motor for all operations to be performed on the cassette and film contained therein. The programming cam disc cooperates with shiftable control components supported on both sides of the plate casting for determining the direction and other characteristics of film travel in the cassette, the positioning and retraction of cassette engaging components and the like. A self-contained sound module may be either incorporated in or left out of the viewer completely without modification of structure or components needed for photographic film processing and/or viewing. Programming cam positioning is effected through a drive train originating with the main drive motor and under the direct control of one of two momentarily energized solenoids required. The programming cam also operates to eject the cassette from the viewer automatically as the viewer is moved to the off position.
Many of the features of the viewer disclosed herein are the subject matter of other applications which are being filed concurrently herewith and which are assigned to the assignee of the present invention. As indicated the present invention is specifically directed to the arrangement in the viewer for controlling the speed of the motor. Prior art U.S. Pat. No. 3,977,623, issued to John P. Bagby et al on Aug. 31, 1976, discloses a mode change system wherein energy is directed to a capacitor during system operation and the system is programmed to a new mode whenever the charge level on the capacitor reaches a predetermined level. An arrangement is included in this prior art system to discharge for capacitor with each revolution of a web coiling spool and then a mode change is effected whenever the spool ceases to rotate.